Tool for machining

ABSTRACT

A tool for machining is made from a hard-metal, cermet or ceramic base material and a single-layer or multi-layer hard material coating on the base material. An additional coating of one or more metals from the group of aluminum, copper, zinc, titanium, nickel, tin or base alloys of these metals is applied to the hard material coating.

CROSS-REFERENCE TO RELATED APPLICATION

This is a continuation, under 35 U.S.C. §120, of copending internationalapplication No. PCT/AT2005/000478, filed Nov. 28, 2005, which designatedthe United States; this application also claims the priority, under 35U.S.C. §119, of Austrian application No. GM 872/2004, filed Dec. 2,2004; the prior applications are herewith incorporated by reference intheir entirety.

BACKGROUND OF THE INVENTION Field of the Invention

The invention relates to a tool for machining made from a hard-metal,cermet or ceramic base material and a single-layer or multi-layer hardmaterial coating applied to the base material.

Tools for machining that are made from hard metal or cermet(ceramic/metal) still do not have the optimum wear resistance and edgelife in many specific machining cases. They are, therefore, additionallyprovided with a single-layer or multi-layer hard material layer.

Examples of such hard material layers are carbidic, nitridic,carbonitridic, oxidic or boridic compounds of various metals andnonmetallic, superhard compounds.

Hard material layers that are used particularly frequently are, forexample, titanium nitride, titanium carbonitride and aluminium oxide,which are used alone or in combination with one another.

To apply these hard material layers, chemical or physical vapordeposition processes, known as CVD (chemical vapor deposition) and PVD(physical vapor deposition) processes, are primarily used.

Depending on the coating processes used, production-induced surfaceroughnesses of the base material to be coated, the crystallinity of thehard materials and process-induced layer growth characteristics as wellas impurities cause undesired microroughnesses on the free surface ofthe coating, which can impair the wear resistance and consequently theedge life of the tool. In order to reduce these surface roughnesses asmuch as possible, and thereby improve the cutting edge stability, suchtools have been subjected to a subsequent smoothing treatment after theapplication of the hard material layer, at least on the free surfaces orcutting edges on which the removed chip runs off. A process that is usedvery often today for the subsequent treatment of the surface of thelayer is the blasting process. In the case of this process, generallygranular abrasives with grain sizes of approximately 1-2000 μm are firedin a dry form by compressed air or in a wet form as a suspension bypositive pressure onto the surface and smoothing of the surface isachieved as a result. Corundum is frequently used as the abrasive.

German patent DE 199 24 422 C2 and its counterpart U.S. Pat. No.6,869,334 B1, for example, describe such a blasting process in whichAl₂O₃ or SiC with grain sizes of 1-100 μm are used in particular as theabrasive and, as a difference from other blasting processes, theabrasive has a sharp-edged grain shape.

A disadvantage of such blasting processes that are used is thatreproduced, controlled removal of thin top layers or of parts of thehard material layers can often only be achieved with difficulty andconsiderable effort. In addition, in the case of the previously knownblasting processes, no color-changing top layer is achieved.

Another possible way of increasing the wear resistance of cutting toolscoated with hard material is to apply soft sliding layers, on which thechip running off slides away, whereby the wear of the tool face isreduced. At the same time, the friction between the flank of the tooland the workpiece is reduced, whereby the wear in the region of the toolflank is also reduced.

International PCT publication WO 96/30148 and its counterpart U.S. Pat.No. 6,213,692 B1, by way of example, describe a cutting tool with whichsulphides, selenides, tellurides or mixed compounds thereof are appliedas corresponding sliding layers.

The disadvantage of such layers is that they usually only have a lowthermal, chemical and mechanical stability with respect to abrasion andsometimes inadequate layer adhesion under the high thermal, chemical andmechanical stresses that occur during machining. In addition, no changein the colouring, and consequently possible improvement in the detectionof wear, is achieved with such layers either.

SUMMARY OF THE INVENTION

It is accordingly an object of the invention to provide a machiningtool, which overcomes the above-mentioned disadvantages of theheretofore-known devices and methods of this general type and which, incomparison with the prior art-type after-treated tools, has improvedwear resistance, and consequently a longer edge life, can be producedcost-effectively and inexpensively, and with which much improveddetection of wear is ensured.

With the foregoing and other objects in view there is provided, inaccordance with the invention, a tool for machining, comprising:

a tool body made of a base material selected from the group consistingof hard-metal, cermet, and ceramic;

a hard material coating applied to said base material; and

an additional coating of one or more metals selected from the groupconsisting of aluminum, copper, zinc, titanium, nickel, tin, or basealloys of the metals applied to said hard material coating.

In other words, the objects are achieved, according to the invention,with an additional coating of one or more metals selected from the groupincluding aluminum, copper, zinc, titanium, nickel, tin or base alloysof these metals being applied to the hard material coating.

Completely surprisingly, it has been found that improved chip flow isachieved by the after-treatment according to the invention, so that, inthe case of dry turning in particular, there is no damage to the cuttingedges, and consequently there is a significant increase in the possibleoperating time of the cutting tool.

Added to this as an advantageous side effect is that the colouring ofthe cutting tool is changed by the metallically bright character and, asa result, the detection of wear is made much easier, in particular inthe case of cutting tools that are provided with a dark-grey ordark-brown or black aluminium oxide layer as the uppermost hard materiallayer.

The coating according to the invention can be advantageously used on allknown hard material layers, such as in the case of layers of carbides,nitrides, carbonitrides or borides of the metals of the group IVa-VIa ofthe periodic table, such as for example Ti, Zr, Hf and combinationsthereof and these together with additives of, for example, oxygen and/orboron, as well as in the case of layers of TiAlN and in the case oflayers that consist entirely or partially of aluminium oxide and/orzirconium oxide.

For the application of the coating according to the invention it ispossible to use, inter alia, known coating processes such as CVD or PVDprocesses as well as other known coating processes.

With regard to an advantageous thickness of the coating according to theinvention, layer thicknesses in the range of 0.05-50 μm, preferably inthe range of 0.1-10 μm, have proven to be successful.

The application of the coating according to the invention is ofadvantage in particular whenever the uppermost layer of the hardmaterial coating comprises a layer containing aluminium oxide, since thedetection of wear is particularly problematic due to the great lightabsorption of the aluminium oxide.

In the case of hard material coatings in which the uppermost layercontains titanium carbide, titanium carbonitride, titanium nitride ortitanium diboride, particularly good results with regard to improvementof the wear resistance are achieved by the application of the additionalcoating according to the invention.

Aluminium and aluminium base alloys, in particular an aluminium basealloy with 12% by weight silicon, and bronze and bronze alloys, which onthe one hand have excellent sliding or lubricating properties and on theother hand outstandingly even out the irregularities of the uppermostlayer of the hard material layer, and consequently significantly improvethe wear behaviour of the tool treated according to the invention, haveproven to be particularly advantageous materials for the coating layersaccording to the invention. In addition, specific changes in the colourof the tool are obtained, making particularly clear detection of wear onthe tool possible by virtue of the great light reflection.

In particular, it is expedient to perform the application of a coatingaccording to the invention in the case of indexable inserts. In thiscase, it is particularly inexpensive and easy to perform the applicationof the coating according to the invention by a blasting treatment usingan abrasive consisting of the desired coating metal.

It may also be of advantage to subject the uppermost hard material layerto a blasting treatment with a nonmetallic abrasive, such as corundumfor example, before the application of the coating according to theinvention. As a result, the surface is already pre-smoothed and theapplication of the coating according to the invention can then beperformed with smaller layer thicknesses.

Apart from this special advantageous pretreatment for smoothing theuppermost hard material layer, it goes without saying that other knownprocesses, such as for example mechanical brushing, abrasive mediaburnishing, etc., can also be used.

Other features which are considered as characteristic for the inventionare set forth in the appended claims.

Although the invention is illustrated and described herein as embodiedin tool for machining, it is nevertheless not intended to be limited tothe details shown, since various modifications and structural changesmay be made therein without departing from the spirit of the inventionand within the scope and range of equivalents of the claims.

The construction and method of operation of the invention, however,together with additional objects and advantages thereof will be bestunderstood from the following description of specific examples when readin connection with the accompanying drawing figures.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

FIGS. 1-5 are magnified views of the cutting edge of indexable cuttinginserts after specified periods of use in a machining operation.

DETAILED DESCRIPTION OF THE INVENTION Example 1

Indexable inserts comprising a hard metal substrate with 5.8% Co, 1%TiC, 0.8% ZrC, 0.2% ZrN, 4.1% TaC, the remainder WC, coated withmultiple layers of an 18 μm thick Ti(C,N)/Al2O3 mixedoxide/Ti(C,N,B)/TiN hard material coating, were blasted for 1 minute ina blasting installation with grit of an aluminium-silicon alloy with 12%by weight silicon and a grain size of 100-315 μm under a pressure of 2.5bar. The indexable inserts were thereby provided with a thin,metallically bright coating.

These indexable inserts coated according to the invention with an Al—Sialloy were used in a machining test for the turning of constructionsteel Ck45, with a strength of 700 N/mm2, at a cutting rate of 300m/min, with a feed rate of 0.25 mm/rev and a cutting depth of 2 mm,without coolant. For purposes of comparison, the same hard materialcoated indexable inserts, but without the coating according to theinvention, were used for turning under the same conditions.

It was thereby found that, with the indexable inserts not coatedaccording to the invention, after turning for only 1 minute the cuttingedges directly next to the wear marks were already damaged. Theseinstances of damage are shown in FIG. 1 by way of example by images ofthe tool face and the tool flank of an indexable insert.

With the indexable inserts coated according to the invention, no damagecould be found on the cutting edge after turning for the same time of 1minute (t=1 min). Reference is had to the image of the indexable insertshown in FIG. 2.

It is evident from this that the edge life of the cutting edge isprolonged by the metallic coating according to the invention.

Example 2

Indexable inserts with the same hard metal substrate/hard material layerconstruction as in Example 1 were blasted for 1 minute in a blastinginstallation with brass grit having a grain size of 100-315 μm under apressure of 2.5 bar.

These indexable inserts coated with brass according to the inventionwere once again subjected to the same machining test as in Example 1together with identical indexable inserts without the brass coatingaccording to the invention and were compared with one another.

In a way similar to that already shown in FIG. 1 by way of example on anindexable insert according to Example 1, after turning for only 1 minute(t=1 min) the indexable inserts not coated according to the inventionwere already damaged on the cutting edges by the running-off chip.

The indexable inserts coated with brass according to the invention didnot exhibit any damage on the cutting edges after turning for the sametime. This is shown in FIG. 3 by way of example on an indexable insert.

Example 3

The same indexable inserts as in Example 1, on the one hand coatedaccording to the invention and on the other hand without an additionalcoating, were used in a second machining test for the turning of steelCk45, with a strength of 700 N/mm2, at a cutting rate of 320 m/min andwith a feed rate of 0.3 mm/rev and a cutting depth of 2 mm, using acooling emulsion.

It was thereby found that, after turning for only 1 minute the indexableinserts coated according to the invention were already damaged on theunderside by the running-off chip in such a way that the cutting edgesat this point of the indexable insert could no longer be used forturning. These instances of damage are shown in FIG. 4 by way of exampleby the images of the tool face of an indexable insert. In the case ofthe indexable inserts coated according to the invention, even afterturning for 6 minutes no damage caused by the running-off chip wasevident at all on the underside, which is shown in FIG. 5 by way ofexample by the image of an indexable insert.

It is evident from these examples that the serviceability of hardmaterial coated tools can be significantly increased by the treatmentfor them according to the invention.

Example 4

Indexable inserts comprising a hard metal substrate with 6% Co, theremainder WC, were coated with a 16 μm thick multi-layer hard materialcoating of Ti(C,N)/Ti(C,N,B)/Al₂O₃ mixed oxide. Subsequently, some ofthe indexable inserts were coated with a coating according to theinvention of an Al—Si coating as in Example 1.

In a comparative machining test, both variants of the indexable insertwere used for the turning of cast ferrous metal GG25, hardness 190 HB,at a cutting rate of 350 m/min, with a feed rate of 0.3 mm/rev and acutting depth of 2 mm, without the use of a cooling emulsion.

The indexable inserts with the coating according to the invention of theAl—Si alloy had on average a 28% higher edge life until the maximumpermissible wear mark width of 0.3 mm was reached.

Example 5

Indexable inserts comprising a hard metal substrate with 6% Co, 2% TaC,the remainder WC, were coated as in Example 4 and some of the insertswere coated with a coating according to the invention of an Al—Si alloyas in Example 1. Both variants of the indexable insert were subjected tothe same comparative machining test as in Example 4.

Indexable inserts with the Al—Si coating according to the invention hadon average a 21% higher edge life until the maximum permissible wearmark width 0.3 mm was reached.

The invention claimed is:
 1. A tool for machining, comprising: a toolbody made of a base material selected from the group consisting ofhard-metal, cermet, and ceramic; a hard material coating applied to saidbase material; and an additional metallic coating of one or more metalsselected from the group consisting of aluminum, copper, zinc, titanium,nickel, tin, or base alloys of the metals applied directly on said hardmaterial coating.
 2. The tool according to claim 1, wherein said hardmaterial coating is a single-layer or a multi-layer hard materialcoating.
 3. The tool according to claim 1, wherein said additionalcoating has a layer thickness in a range from 0.05 to 50 μm.
 4. The toolaccording to claim 3, wherein the layer thickness of said additionallayer is between 0.1 and 10 μm.
 5. The tool according to claim 1,wherein said hard material coating has an uppermost layer containingaluminum oxide.
 6. The tool according to claim 1, wherein said hardmaterial coating has an uppermost layer containing titanium carbide,titanium carbonitride, titanium nitride, or titanium boride.
 7. The toolaccording to claim 1, wherein said additional coating consists ofaluminum or a base alloy of aluminum.
 8. The tool according to claim 1,wherein said additional coating consists of an aluminum base alloy with12% by weight silicon.
 9. The tool according to claim 1, wherein saidadditional coating consists of a brass or bronze alloy.
 10. The toolaccording to claim 1, wherein said tool body is configured to form anindexable insert.
 11. The tool according to claim 1, wherein saidadditional coating is a substantially pure metallic coating.
 12. A toolfor machining, comprising: a tool body made of a base material selectedfrom the group consisting of hard-metal, cermet, and ceramic, and havingat least one machining tool cutting edge; a hard material coatingapplied to said base material; and an additional metallic coating of oneor more metals selected from the group consisting of aluminum, copper,zinc, titanium, nickel, tin, or base alloys of the metals applieddirectly on said hard material coating; and wherein said tool body, saidhard material coating, and said additional metallic coating togetherform a machining tool with a surface that is resistant to thermal,chemical, and mechanical stresses that occur during machining.
 13. Amethod for producing a machining tool according to claim 1, whichcomprises providing a tool body coated with a hard material layer, andapplying an additional coating by performing a blasting treatment of anuppermost layer of the hard material layer, and using granular abrasiveswith a desired composition of the additional coating in the blastingtreatment.
 14. A method for producing a machining tool according toclaim 1, which comprises providing a tool body coated with a hardmaterial, subjecting an uppermost hard material layer to a blastingtreatment with a nonmetallic abrasive, and subsequently applying anadditional coating.
 15. The method according to claim 14, whichcomprising comprises blasting the hard material with corundum.